Vapor treatment of metals.



WILLIAM A. DARRAH AND SAMUEL TROOD, OF WILKINSBTTRG, PENNSYLVANIA, ASSIGNORS TO INDUSTRIAL DEVELOPMENT COMPANY, A CORPORATION OF VAPOR TREATMENT OF METALS.

To all whom it may concern:

Be it known that We, WILLIAM A. DAnnAi-r and SAMUEL Tnooo, citizens of the United to change the qualities of a metal by the addition of other metals or other substances,

' and it may be expedient for reasons of cost, or otherwise to effect this addition after the metal is brought into the final form; in other words, under conditions such that a surface alloy or compound is preferable to a homogeneous metal. Our invention, therefore comprises a method of forming a surface compound or alloy which possesses the desired properties. Thus we may treat iron so that the outer layer w1ll be rust proof; we may treat copper or iron, etc., so that its outer layer will be extremely hard or extremely tough, or resist certain agents, etc. i

The depth to which this process is applicable, is of course dependent upon the surrounding conditions, as will be later explained.

It is a well known fact that all common metals are extremely porous. This is visible with the magnifying glass as well as readily demonstrated by certain physical experiments. Thus, if an iron wire be placed in an exhaust tube, and then heated to incandescence, as for instance, by passing a current through the wire, the pressure within the tube rises materially, and gas is evolved for a very considerable time, indicating that iron (and practically all other metals), contain large volumes of gases. The condition of the metal may be graphically described as resembling a sponge soaked with water.

There also appears to be an electrical c0n-- dition accompanying the evolution of gases from a metal, inasmuch as we have found that the evolved gases usually contain a number of free ions. This is particularly the case if the temperature of the metal is high at the time the gases are given out.

Patented May 1, 1917.

PENNSYLVANIA.

.1,224 ,339 Specification of Letters Patent.

No Drawing.

Application filed April 4, 1914. Serial No. 829,662.

Naturally the exposed surface of a metal, is the only portion which activcly takes part in evolving or absorbing gases, so that the larger the area of the surface exposed, the greater the evolution of gas, other conditions being equal.

Now it is a well known fact that all materials have a definite vapor pressure, depending mainly on the nature of the material, the nature of the surrounding matorials, the temperature and the pressure. It therefore follows, that under all conditions, all substances are surrounded by a certain amount of their own vapor. The vapor can be increased in amount by increasing the temperature and decreasing the pressure. This is well illustrated by the so called triple point condition of a substance at which point the material can exist simultaneously as a solid liquid and gas. On lowering the pressure, it is possible in many cases to cause a solid to pass directly from a solid to a gas.

A further fact which is well established is that the presence of free ions has a marked efiect in producing a condensation of a vapor or suspended matter in a gas.

It follows, therefore, that if a metal be heated in the presence of a vapor under such conditions that the gases or vapors contained within the metal are in part liberated, then as these liberated gases or vapors contain some free ions, they will cause the precipitation within the pores of the metal and on the surface layer of a portion of the external vapor in which the metal is heated.

It must be understood of course, that while the above theory explains the reactions which we are able to produce, yet we are not certain of its accuracy. Furthermore, since this invention comprises a process of treating metals, we do not'desire to be confined to any particular theory, but only to the process which we have devised.

The process as well as the theory described above, may be well illustratedby the specific case of the treatment of iron with aluminum, which is used only as an example. If a piece of iron is placed in a closed air tight vessel, powdered metallic aluminum, and the temperature raised to even 1000 C. no material surrounded by change can be noted in the iron, and the amount of aluminum thus absorbed in a few hours is so small as to be negligible as far as any effect upon the properties of the iron is concerned. ing the temperature, the pressure within the vessel is reduced by removing the air an appreciable amount of aluminum will pass into the surface layer of the iron. Under these conditions, a very appreciable effect can be produced if the temperature does not exceed 7 00 C. and the vacuum is suliicient to support 20 inches of mercury. These conditions are of course to be considered as merely examples, as copper, brass, platinum, and many other metals may be substituted for the iron and sodium, calcium, zinc, etc., may be substituted for the aluminum or even such substances may beused as sulfur, arsenic, antimony, phosphorus, silicon, carbon, boron and some of their compounds.

In the case of the aluminum treated iron, the result is a rust proof metal having all of the qualities of a very high grade steel or iron, but much more permanent than galvanizing or similar treatments.

In view of the above facts, it appears that when a metal is heated in the presence of the vapor of another metal, or the vapor of. other elements or compounds, the metal evolves a portion of the gases or vapor which it contains, and in exchange condenses some of the other vapors within its pores.

Iron heated with powdered antimony to a temperature below the melting point of the latter for several hours at a reduced pressure, gives an excellent rust resisting surface layer. A vacuum of twenty-six inches of mercury gives very good results in this case, although it is not necessary to reduce the pressure as much as this. As will be evident, however, a reduced pressure will hasten the process with a given temperature, or if the same time is allowed, a reduced pressure Will allow a reduction in temperature.

The process which we have devised is not necessarily dependent upon having the substances supplying the vapor in the form of a powder, as in the example illustrated, although a substance in this form may often be raised to a temperature above the melting point without fusing the articles together. The elevated temperature which can thus be secured is of material assistance in securing a rich vapor which naturally hastens the process and therefore is an advantage in many cases. A further advantage of using the material supplying the vapor in the powdered form is the enormously increased surface which can thus be Secured, thus giving a richer vapor, since If now, in addition to raisthe amount of material vaporized at a given temperature and pressure increases with increased evaporating surface. ticularly of value when the boiling point of the vapor giving material is above the temperature. at which the deposition occurs.

The temperatures Which we have found effective in the case of depositingaluminum vapor in iron is a full-red heat. We do not desire to be limited to this temperature, however, as each material used to supply the vapor, as well as each material absorbing the vapor, and each combination of vapor giving material with vapor absorbing material may require a different temperature for securing most satisfactory results.

A further point Which should be noted is that the evolution of gas from the absorbing substance appears to function in the absorption, so that by the medium of evolved gas, it is possible to cause the condensation of one substance within the pores or surface layer of another at a temperature which is actually below the melting point of the material deposited. We have also found that the evolved gas need not beheld in the metal purely by physical combination, as gases which are liberated by a chemical action such as a decomposition reduction of an oxid, or formation of a compound, are also effective. The process which we employ may thus be made more efiective in some cases by putting the vapor absorbing material in a condition such that when raised to the proper temperature and proper pressure, a considerable amount of gas or vapor will be evolved. One method of causing this is to make the material the pole of an elec- This is partrolytic cell at which hydrogen is evolved.

Under these conditions, sufficient gas will be absorbed by the metal to assist in the subsequent vapor treatment.

From the above description, it will be evident that our process comprises essentially the heating of metal to be treated in the presence of the vapor to beabsorbed for a given time and at a reduced pressure. The exact value of temperature, pressure and. time depend of course upon the materials used and other conditions as set forth.

Actual experience with the described has developed the fact that the surface combination may be effected without the contact in the solid form of the treating material with the surface to be treated. Thus a portion of zinc dust may be placed in, one part of the vacuum chamber, the iron to be treated in another portion of the chamber and the reaction will proceed on sufliciently reducing the pressure and applying the necessary heat, although of course the zinc and iron are in substantial contact.

process here Having described our invention what we claim as new and desire to secure by Letters Patent is 1.. The process of forming a compound in a metal by heating the metal under reduced pressure in the presence of the vapor of the compound formlng material.

2. The process of forming an alloy of a metal by heating the metal under reduced pressure in the presence of the vapor of the alloy forming metal.

3. The process of forming an iron alloy by heating the iron under reduced pressure in the presence of the vapor of the alloy forming material.

4. The process of condensing a vapor within a metal by surrounding the metal while heated, by the desired vapor at a pressure below atmospheric pressure.

5. The process of forming a coating of zinc upon iron by heating the said iron in the presence of zinc vapor under reduced pressure in a chamber from which other gases and vapors have been substantially exhausted.

6. The process of depositing zinc on iron by heating the iron and zinc dust together removing all vapors and under reduced pressure in a chamber from which other vapors than zinc have been substantially exhausted.

7. The process of condensing a vapor within a metal by heating the metal in the presence of the desired vapor in a chamber from which other gases and vapors have been substantially exhausted, the pressure within said chamber being maintained lower than atmospheric.

8. The process of condensing a vapor upon a metal which consists in placing said metal in a chamber in the presence of the material to supply the desired vapor, substantially gases but those due to the treating material and heating said chamber while the contents are maintained at a pressure lower than atmospheric.

In testimony whereof, we have hereunto subscribed our names this third day of April 1914.

WILLIAM A. DARRAI-I. SAMUEL TROOD.

Witnesses:

A. QH MYTHoFF, D. A. BARBOR. 

